| 360661 |
05-May-2020 |
dim |
Merge llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and openmp
9.0.1 final release c1a0a213378a458fbea1a5c77b315c7dce08fd05, and a
number of follow-ups.
MFC r355948:
Bootstrap mergeinfo for contrib/llvm-project
Merge (record-only) the following paths to contrib/llvm-project:
* ^/vendor/llvm-project/master
* ^/vendor/llvm-project/release-8.x
* ^/vendor/llvm-project/release-9.x
MFC r355951:
Merge empty dir updates from r355950 in vendor/llvm-project.
MFC r355957:
Merge diff elimination updates from r355953 into vendor/llvm-project.
MFC r355959:
Consolidate FREEBSD-Xlist files of different llvm sub-projects into one.
MFC r356004:
Merge llvm, clang, compiler-rt, libc++, libunwind, lld, lldb and openmp
9.0.1 final release c1a0a213378a458fbea1a5c77b315c7dce08fd05.
Release notes for llvm, clang, lld and libc++ 9.0.1 will become
available here:
https://releases.llvm.org/9.0.1/docs/ReleaseNotes.html
https://releases.llvm.org/9.0.1/tools/clang/docs/ReleaseNotes.html
https://releases.llvm.org/9.0.1/tools/lld/docs/ReleaseNotes.html
https://releases.llvm.org/9.0.1/projects/libcxx/docs/ReleaseNotes.html
PR: 240629
MFC r356005:
Merge commit f97936fab from llvm git (by Eric Fiselier):
[libc++] Cleanup and enable multiple warnings.
Too many warnings are being disabled too quickly. Warnings are
important to keeping libc++ correct. This patch re-enables two
warnings: -Wconstant-evaluated and -Wdeprecated-copy.
In future, all warnings disabled for the test suite should require an
attached bug. The bug should state the plan for re-enabling that
warning, or a strong case why it should remain disabled.
This should fix a number of new g++ 9 warnings.
Requested by: rlibby
MFC r356100:
Merge commit d3aeac8e2 from llvm git (by Justin Hibbits)
[PowerPC] Only use PLT annotations if using PIC relocation model
Summary:
The default static (non-PIC, non-PIE) model for 32-bit powerpc does
not use @PLT annotations and relocations in GCC. LLVM shouldn't use
@PLT annotations either, because it breaks secure-PLT linking with
(some versions of?) GNU LD.
Update the available-externally.ll test to reflect that default mode
should be the same as the static relocation, by using the same check
prefix.
Reviewed by: sfertile
Differential Revision: https://reviews.llvm.org/D70570
Reviewed by: jhibbits
Differential Revision: https://reviews.freebsd.org/D22913
MFC r356104 (by jhibbits):
[PowerPC] enable atomic.c in compiler_rt and do not check and forces
lock/lock_free decisions in compiled time
Summary:
Enables atomic.c in compiler_rt and forces clang to not emit a call for runtime
decision about lock/lock_free. At compiling time, if clang can't decide if
atomic operation can be lock free, it emits calls to external functions like
`__atomic_is_lock_free`, `__c11_atomic_is_lock_free` and
`__atomic_always_lock_free`, postponing decision to a runtime check. According
to LLVM code documentation, the mechanism exists due to differences between
x86_64 processors that can't be decided at runtime.
On PowerPC and PowerPCSPE (32 bits), we already know in advance it can't be lock
free, so we force the decision at compile time and avoid having to implement it
in an external library.
This patch was made after 32 bit users testing the PowePC32 bit ISO reported
llvm could not be compiled with in-base llvm due to `__atomic_load8` not
implemented.
Submitted by: alfredo.junior_eldorado.org.br
Reviewed by: jhibbits, dim
Differential Revision: https://reviews.freebsd.org/D22549
MFC r356112 (by jhibbits):
[PowerPC64] Starting from FreeBSD 13.0, default to ELFv2 ABI
This changes the LLVM default powerpc64 ABI to ELFv2, if target OS is
FreeBSD >= 13.0
This will also be sent upstream.
Submitted by: alfredo.junior_eldorado.org.br
Reviewed by: dim, luporl
Relnotes: YES
Differential Revision: https://reviews.freebsd.org/D20383
MFC r356256:
Merge commit 468a0cb5f from llvm git (by Craig Topper):
[X86] Add X87 FCMOV support to X86FlagsCopyLowering.
Fixes PR44396
Merge commit 86f48999f from llvm git (by Craig Topper):
[X86] Fix typo in getCMovOpcode.
The 64-bit HasMemoryOperand line was using CMOV32rm instead of
CMOV64rm. Not sure how to test this. We have no test coverage that
passes true for HasMemoryOperand.
This fixes 'Assertion failed: (MI.findRegisterDefOperand(X86::EFLAGS) &&
"Expected a def of EFLAGS for this instruction!"), function
runOnMachineFunction' when compiling the misc/gpsim port for i386.
Reported by: yuri
Upstream PR: https://bugs.llvm.org/show_bug.cgi?id=44396
MFC r356329:
Merge commit 41449c58c from llvm git (by Roger Ferrer Ibanez):
[RISCV] Fix evaluation of %pcrel_lo
The following testcase
function:
.Lpcrel_label1:
auipc a0, %pcrel_hi(other_function)
addi a1, a0, %pcrel_lo(.Lpcrel_label1)
.p2align 2 # Causes a new fragment to be emitted
.type other_function,@function
other_function:
ret
exposes an odd behaviour in which only the %pcrel_hi relocation is
evaluated but not the %pcrel_lo.
$ llvm-mc -triple riscv64 -filetype obj t.s | llvm-objdump -d -r -
<stdin>: file format ELF64-riscv
Disassembly of section .text:
0000000000000000 function:
0: 17 05 00 00 auipc a0, 0
4: 93 05 05 00 mv a1, a0
0000000000000004: R_RISCV_PCREL_LO12_I other_function+4
0000000000000008 other_function:
8: 67 80 00 00 ret
The reason seems to be that in RISCVAsmBackend::shouldForceRelocation
we only consider the fragment but in RISCVMCExpr::evaluatePCRelLo we
consider the section. This usually works but there are cases where
the section may still be the same but the fragment may be another
one. In that case we end forcing a %pcrel_lo relocation without any
%pcrel_hi.
This patch makes RISCVAsmBackend::shouldForceRelocation use the
section, if any, to determine if the relocation must be forced or
not.
Differential Revision: https://reviews.llvm.org/D60657
This is a prerequisite for building and linking hard- and soft-float
riscv worlds with clang and lld.
Requested by: jhb
MFC r356330:
Merge commit da7b129b1 from llvm git (by James Clarke):
[RISCV] Don't force Local Exec TLS for non-PIC
Summary:
Forcing Local Exec TLS requires the use of copy relocations. Copy
relocations need special handling in the runtime linker when being
used against TLS symbols, which is present in glibc, but not in
FreeBSD nor musl, and so cannot be relied upon. Moreover, copy
relocations are a hack that embed the size of an object in the ABI
when it otherwise wouldn't be, and break protected symbols (which are
expected to be DSO local), whilst also wasting space, thus they
should be avoided whenever possible. As discussed in D70398, RISC-V
should move away from forcing Local Exec, and instead use Initial
Exec like other targets, with possible linker relaxation to follow.
The RISC-V GCC maintainers also intend to adopt this
more-conventional behaviour (see
https://github.com/riscv/riscv-elf-psabi-doc/issues/122).
Reviewers: asb, MaskRay
Reviewed By: MaskRay
Subscribers: emaste, krytarowski, hiraditya, rbar, johnrusso,
simoncook, sabuasal, niosHD, kito-cheng, shiva0217, zzheng,
edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o, rkruppe,
PkmX, jocewei, psnobl, benna, Jim, lenary, s.egerton, pzheng,
sameer.abuasal, apazos, llvm-commits, bsdjhb
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70649
This is a prerequisite for building and linking hard- and soft-float
riscv worlds with clang and lld.
Requested by: jhb
MFC r356331:
?Merge commit c6b09bff5 from llvm git (by Lu?s Marques):
[RISCV] Fix wrong CFI directives
Summary: Removes CFI CFA directives that could incorrectly propagate
beyond the basic block they were inteded for. Specifically it removes
the epilogue CFI directives. See the branch_and_tail_call test for an
example of the issue. Should fix the stack unwinding issues caused by
the incorrect directives.
Reviewers: asb, lenary, shiva0217
Reviewed By: lenary
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D69723
This is a prerequisite for building and linking hard- and soft-float
riscv worlds with clang and lld.
Requested by: jhb
MFC r356332:
?Merge commit d7be3eab5 from llvm git (by Lu?s Marques):
[RISCV] Handle fcopysign(f32, f64) and fcopysign(f64, f32)
Summary: Adds tablegen patterns to explicitly handle fcopysign where
the magnitude and sign arguments have different types, due to the
sign value casts being removed the by DAGCombiner. Support for RV32IF
follows in a separate commit. Adds tests for all relevant scenarios
except RV32IF.
Reviewers: lenary
Reviewed By: lenary
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D70678
This is a prerequisite for building and linking hard- and soft-float
riscv worlds with clang and lld.
Requested by: jhb
MFC r356333:
?Merge commit 189b7393d from llvm git (by John Baldwin):
[lld][RISCV] Use an e_flags of 0 if there are only binary input files.
Summary:
If none of the input files are ELF object files (for example, when
generating an object file from a single binary input file via "-b
binary"), use a fallback value for the ELF header flags instead of
crashing with an assertion failure.
Reviewers: MaskRay, ruiu, espindola
Reviewed By: MaskRay, ruiu
Subscribers: kevans, grimar, emaste, arichardson, asb, rbar,
johnrusso, simoncook, sabuasal, niosHD, kito-cheng, shiva0217,
zzheng, edward-jones, rogfer01, MartinMosbeck, brucehoult, the_o,
rkruppe, PkmX, jocewei, psnobl, benna, Jim, lenary, s.egerton,
pzheng, sameer.abuasal, apazos, luismarques, llvm-commits, jrtc27
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D71101
This is a prerequisite for building and linking hard- and soft-float
riscv worlds with clang and lld.
Requested by: jhb
MFC r356701:
Merge commit f46ba4f07 from llvm git (by Simon Atanasyan):
[mips] Use less registers to load address of TargetExternalSymbol
There is no pattern matched `add hi, (MipsLo texternalsym)`. As a
result, loading an address of 32-bit symbol requires two registers
and one more additional instruction:
```
addiu $1, $zero, %lo(foo)
lui $2, %hi(foo)
addu $25, $2, $1
```
This patch adds the missed pattern and enables generation more
effective set of instructions:
```
lui $1, %hi(foo)
addiu $25, $1, %lo(foo)
```
Differential Revision: https://reviews.llvm.org/D66771
llvm-svn: 370196
Merge commit 59bb3609f from llvm git (by Simon Atanasyan):
[mips] Fix 64-bit address loading in case of applying 32-bit mask to
the result
If result of 64-bit address loading combines with 32-bit mask, LLVM
tries to optimize the code and remove "redundant" loading of upper
32-bits of the address. It leads to incorrect code on MIPS64 targets.
MIPS backend creates the following chain of commands to load 64-bit
address in the `MipsTargetLowering::getAddrNonPICSym64` method:
```
(add (shl (add (shl (add %highest(sym), %higher(sym)),
16),
%hi(sym)),
16),
%lo(%sym))
```
If the mask presents, LLVM decides to optimize the chain of commands.
It really does not make sense to load upper 32-bits because the
0x0fffffff mask anyway clears them. After removing redundant commands
we get this chain:
```
(add (shl (%hi(sym), 16), %lo(%sym))
```
There is no patterns matched `(MipsHi (i64 symbol))`. Due a bug in
`SYM_32` predicate definition, backend incorrectly selects a pattern
for a 32-bit symbols and uses the `lui` instruction for loading
`%hi(sym)`.
As a result we get incorrect set of instructions with unnecessary
16-bit left shifting:
```
lui at,0x0
R_MIPS_HI16 foo
dsll at,at,0x10
daddiu at,at,0
R_MIPS_LO16 foo
```
This patch resolves two problems:
- Fix `SYM_32/SYM_64` predicates to prevent selection of patterns
dedicated to 32-bit symbols in case of using N64 ABI.
- Add missed patterns for 64-bit symbols for `%hi/%lo`.
Fix PR42736.
Differential Revision: https://reviews.llvm.org/D66228
llvm-svn: 370268
These two commits fix a miscompilation of the kernel for mips64, and
should allow clang to be used as the default compiler for mips64.
Requested by: arichards
MFC r356789 (by arichardson):
Merge commit 894f742acb from llvm git (by me):
[MIPS][ELF] Use PC-relative relocations in .eh_frame when possible
When compiling position-independent executables, we now use
DW_EH_PE_pcrel | DW_EH_PE_sdata4. However, the MIPS ABI does not define a
64-bit PC-relative ELF relocation so we cannot use sdata8 for the large
code model case. When using the large code model, we fall back to the
previous behaviour of generating absolute relocations.
With this change clang-generated .o files can be linked by LLD without
having to pass -Wl,-z,notext (which creates text relocations).
This is simpler than the approach used by ld.bfd, which rewrites the
.eh_frame section to convert absolute relocations into relative references.
I saw in D13104 that apparently ld.bfd did not accept pc-relative relocations
for MIPS ouput at some point. However, I also checked that recent ld.bfd
can process the clang-generated .o files so this no longer seems true.
Reviewed By: atanasyan
Differential Revision: https://reviews.llvm.org/D72228
Merge commit 8e8ccf47 from llvm git (by me)
[MIPS] Don't emit R_(MICRO)MIPS_JALR relocations against data symbols
The R_(MICRO)MIPS_JALR optimization only works when used against functions.
Using the relocation against a data symbol (e.g. function pointer) will
cause some linkers that don't ignore the hint in this case (e.g. LLD prior
to commit 5bab291) to generate a relative branch to the data symbol
which crashes at run time. Before this patch, LLVM was erroneously emitting
these relocations against local-dynamic TLS function pointers and global
function pointers with internal visibility.
Reviewers: atanasyan, jrtc27, vstefanovic
Reviewed By: atanasyan
Differential Revision: https://reviews.llvm.org/D72571
These two changes should allow using lld for MIPS64 (and maybe also MIPS32)
by default.
The second commit is not strictly necessary for clang+lld since LLD9 will
not perform the R_MIPS_JALR optimization (it was only added for 10) but it
is probably required in order to use recent ld.bfd.
Reviewed By: dim, emaste
Differential Revision: https://reviews.freebsd.org/D23203
MFC r356929:
Merge commit bc4bc5aa0 from llvm git (by Justin Hibbits):
Add 8548 CPU definition and attributes
8548 CPU is GCC's name for the e500v2, so accept this in clang. The
e500v2 doesn't support lwsync, so define __NO_LWSYNC__ for this as
well, as GCC does.
Differential Revision: https://reviews.llvm.org/D67787
Merge commit ff0311c4b from llvm git (by Justin Hibbits):
[PowerPC]: Add powerpcspe target triple subarch component
Summary:
This allows the use of '-target powerpcspe-unknown-linux-gnu' or
'powerpcspe-unknown-freebsd' to be used, instead of '-target
powerpc-unknown-linux-gnu -mspe'.
Reviewed By: dim
Differential Revision: https://reviews.llvm.org/D72014
Merge commit ba91dffaf from llvm git (by Fangrui Song):
[Driver][PowerPC] Move powerpcspe logic from cc1 to Driver
Follow-up of D72014. It is more appropriate to use a target feature
instead of a SubTypeArch to express the difference.
Reviewed By: #powerpc, jhibbits
Differential Revision: https://reviews.llvm.org/D72433
commit 36eedfcb3 from llvm git (by Justin Hibbits):
[PowerPC] Fix powerpcspe subtarget enablement in llvm backend
Summary:
As currently written, -target powerpcspe will enable SPE regardless
of disabling the feature later on in the command line. Instead,
change this to just set a default CPU to 'e500' instead of a generic
CPU.
As part of this, add FeatureSPE to the e500 definition.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D72673
These are needed to unbreak the build for powerpcspe.
Requested by: jhibbits
MFC r358711:
Merge commit f75939599 from llvm git (by Erich Keane):
Reland r374450 with Richard Smith's comments and test fixed.
The behavior from the original patch has changed, since we're no
longer allowing LLVM to just ignore the alignment. Instead, we're
just assuming the maximum possible alignment.
Differential Revision: https://reviews.llvm.org/D68824
llvm-svn: 374562
This fixes 'Assertion failed: (Alignment != 0 && "Invalid Alignment"),
function CreateAlignmentAssumption', when building recent versions of
v8, which invoke __builtin_assume_aligned() with its alignment argument
set to 4GiB or more.
Clang will now report a warning, and show the maximum possible alignment
instead, e.g.:
huge-align.cpp:1:27: warning: requested alignment must be 536870912 bytes or smaller; maximum alignment assumed [-Wbuiltin-assume-aligned-alignment]
void *f(void *g) { return __builtin_assume_aligned(g, 4294967296); }
^ ~~~~~~~~~~
Upstream PR: https://bugs.llvm.org/show_bug.cgi?id=43839
Reported by: cem |
| 345349 |
20-Mar-2019 |
dim |
Pull in r352826 from upstream lld trunk (by Fangrui Song):
[ELF] Support --{,no-}allow-shlib-undefined
Summary:
In ld.bfd/gold, --no-allow-shlib-undefined is the default when
linking an executable. This patch implements a check to error on
undefined symbols in a shared object, if all of its DT_NEEDED entries
are seen.
Our approach resembles the one used in gold, achieves a good balance
to be useful but not too smart (ld.bfd traces all DSOs and emulates
the behavior of a dynamic linker to catch more cases).
The error is issued based on the symbol table, different from
undefined reference errors issued for relocations. It is most
effective when there are DSOs that were not linked with -z defs (e.g.
when static sanitizers runtime is used).
gold has a comment that some system libraries on GNU/Linux may have
spurious undefined references and thus system libraries should be
excluded (https://sourceware.org/bugzilla/show_bug.cgi?id=6811). The
story may have changed now but we make --allow-shlib-undefined the
default for now. Its interaction with -shared can be discussed in the
future.
Reviewers: ruiu, grimar, pcc, espindola
Reviewed By: ruiu
Subscribers: joerg, emaste, arichardson, llvm-commits
Differential Revision: https://reviews.llvm.org/D57385
Pull in r352943 from upstream lld trunk (by Fangrui Song):
[ELF] Default to --no-allow-shlib-undefined for executables
Summary:
This follows the ld.bfd/gold behavior.
The error check is useful as it captures a common type of ld.so
undefined symbol errors as link-time errors:
// a.cc => a.so (not linked with -z defs)
void f(); // f is undefined
void g() { f(); }
// b.cc => executable with a DT_NEEDED entry on a.so
void g();
int main() { g(); }
// ld.so errors when g() is executed (lazy binding) or when the program is started (-z now)
// symbol lookup error: ... undefined symbol: f
Reviewers: ruiu, grimar, pcc, espindola
Reviewed By: ruiu
Subscribers: llvm-commits, emaste, arichardson
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D57569
Together, these add support for --no-allow-shlib-undefined, and make it
the default for executables, so they will fail to link if any symbols
from needed shared libraries are undefined.
Reported by: jbeich
PR: 236062, 236141
MFC after: 1 month
X-MFC-With: r344779
|
| 328817 |
02-Feb-2018 |
dim |
Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
6.0.0 (branches/release_60 r324090).
This introduces retpoline support, with the -mretpoline flag. The
upstream initial commit message (r323155 by Chandler Carruth) contains
quite a bit of explanation. Quoting:
Introduce the "retpoline" x86 mitigation technique for variant #2 of
the speculative execution vulnerabilities disclosed today,
specifically identified by CVE-2017-5715, "Branch Target Injection",
and is one of the two halves to Spectre.
Summary:
First, we need to explain the core of the vulnerability. Note that
this is a very incomplete description, please see the Project Zero
blog post for details:
https://googleprojectzero.blogspot.com/2018/01/reading-privileged-memory-with-side.html
The basis for branch target injection is to direct speculative
execution of the processor to some "gadget" of executable code by
poisoning the prediction of indirect branches with the address of
that gadget. The gadget in turn contains an operation that provides a
side channel for reading data. Most commonly, this will look like a
load of secret data followed by a branch on the loaded value and then
a load of some predictable cache line. The attacker then uses timing
of the processors cache to determine which direction the branch took
*in the speculative execution*, and in turn what one bit of the
loaded value was. Due to the nature of these timing side channels and
the branch predictor on Intel processors, this allows an attacker to
leak data only accessible to a privileged domain (like the kernel)
back into an unprivileged domain.
The goal is simple: avoid generating code which contains an indirect
branch that could have its prediction poisoned by an attacker. In
many cases, the compiler can simply use directed conditional branches
and a small search tree. LLVM already has support for lowering
switches in this way and the first step of this patch is to disable
jump-table lowering of switches and introduce a pass to rewrite
explicit indirectbr sequences into a switch over integers.
However, there is no fully general alternative to indirect calls. We
introduce a new construct we call a "retpoline" to implement indirect
calls in a non-speculatable way. It can be thought of loosely as a
trampoline for indirect calls which uses the RET instruction on x86.
Further, we arrange for a specific call->ret sequence which ensures
the processor predicts the return to go to a controlled, known
location. The retpoline then "smashes" the return address pushed onto
the stack by the call with the desired target of the original
indirect call. The result is a predicted return to the next
instruction after a call (which can be used to trap speculative
execution within an infinite loop) and an actual indirect branch to
an arbitrary address.
On 64-bit x86 ABIs, this is especially easily done in the compiler by
using a guaranteed scratch register to pass the target into this
device. For 32-bit ABIs there isn't a guaranteed scratch register
and so several different retpoline variants are introduced to use a
scratch register if one is available in the calling convention and to
otherwise use direct stack push/pop sequences to pass the target
address.
This "retpoline" mitigation is fully described in the following blog
post: https://support.google.com/faqs/answer/7625886
We also support a target feature that disables emission of the
retpoline thunk by the compiler to allow for custom thunks if users
want them. These are particularly useful in environments like
kernels that routinely do hot-patching on boot and want to hot-patch
their thunk to different code sequences. They can write this custom
thunk and use `-mretpoline-external-thunk` *in addition* to
`-mretpoline`. In this case, on x86-64 thu thunk names must be:
```
__llvm_external_retpoline_r11
```
or on 32-bit:
```
__llvm_external_retpoline_eax
__llvm_external_retpoline_ecx
__llvm_external_retpoline_edx
__llvm_external_retpoline_push
```
And the target of the retpoline is passed in the named register, or in
the case of the `push` suffix on the top of the stack via a `pushl`
instruction.
There is one other important source of indirect branches in x86 ELF
binaries: the PLT. These patches also include support for LLD to
generate PLT entries that perform a retpoline-style indirection.
The only other indirect branches remaining that we are aware of are
from precompiled runtimes (such as crt0.o and similar). The ones we
have found are not really attackable, and so we have not focused on
them here, but eventually these runtimes should also be replicated for
retpoline-ed configurations for completeness.
For kernels or other freestanding or fully static executables, the
compiler switch `-mretpoline` is sufficient to fully mitigate this
particular attack. For dynamic executables, you must compile *all*
libraries with `-mretpoline` and additionally link the dynamic
executable and all shared libraries with LLD and pass `-z
retpolineplt` (or use similar functionality from some other linker).
We strongly recommend also using `-z now` as non-lazy binding allows
the retpoline-mitigated PLT to be substantially smaller.
When manually apply similar transformations to `-mretpoline` to the
Linux kernel we observed very small performance hits to applications
running typic al workloads, and relatively minor hits (approximately
2%) even for extremely syscall-heavy applications. This is largely
due to the small number of indirect branches that occur in
performance sensitive paths of the kernel.
When using these patches on statically linked applications,
especially C++ applications, you should expect to see a much more
dramatic performance hit. For microbenchmarks that are switch,
indirect-, or virtual-call heavy we have seen overheads ranging from
10% to 50%.
However, real-world workloads exhibit substantially lower performance
impact. Notably, techniques such as PGO and ThinLTO dramatically
reduce the impact of hot indirect calls (by speculatively promoting
them to direct calls) and allow optimized search trees to be used to
lower switches. If you need to deploy these techniques in C++
applications, we *strongly* recommend that you ensure all hot call
targets are statically linked (avoiding PLT indirection) and use both
PGO and ThinLTO. Well tuned servers using all of these techniques saw
5% - 10% overhead from the use of retpoline.
We will add detailed documentation covering these components in
subsequent patches, but wanted to make the core functionality
available as soon as possible. Happy for more code review, but we'd
really like to get these patches landed and backported ASAP for
obvious reasons. We're planning to backport this to both 6.0 and 5.0
release streams and get a 5.0 release with just this cherry picked
ASAP for distros and vendors.
This patch is the work of a number of people over the past month:
Eric, Reid, Rui, and myself. I'm mailing it out as a single commit
due to the time sensitive nature of landing this and the need to
backport it. Huge thanks to everyone who helped out here, and
everyone at Intel who helped out in discussions about how to craft
this. Also, credit goes to Paul Turner (at Google, but not an LLVM
contributor) for much of the underlying retpoline design.
Reviewers: echristo, rnk, ruiu, craig.topper, DavidKreitzer
Subscribers: sanjoy, emaste, mcrosier, mgorny, mehdi_amini, hiraditya, llvm-commits
Differential Revision: https://reviews.llvm.org/D41723
MFC after: 3 months
X-MFC-With: r327952
PR: 224669
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